A pH recorder shows 10.0 when a pH of 8.0 is desired. What should be checked first to diagnose the issue?

When a pH recorder displays a reading significantly different from the desired pH level, the first thing to check is typically the sensor. The sensor, or electrode, is the component that directly measures the pH level of the solution. If the sensor is faulty, damaged, or not functioning properly, it can produce inaccurate readings, such as showing a pH of 10.0 when the true pH is 8.0.

Assessing the sensor first is crucial because it provides immediate insights into whether the problem lies with the measurement equipment itself. If the sensor is not working correctly, no amount of calibration or adjustments to other factors will yield accurate results. This is why it is considered a priority in troubleshooting pH measurement issues.

Other factors such as calibration settings, water temperature, and electrode cleanliness are also important in maintaining accurate pH readings, but they would typically come after confirming that the sensor is in good working condition.